Rainbow is a collaborative album between Japanese experimental rock band Boris and psychedelic guitarist Michio Kurihara. Wata contributed vocals to the title song, which has a music video made for it by Foodunited.
The album's initial release was done by Pedal Records, with liner notes in Portuguese. Drag City released this album in the United States on May 15, 2007 with a different 9th track, on CD format only.
In 2007, Rainbow was also released on vinyl in two forms by Inoxia Records. One, an unlimited LP which contains the album (same as Pedal CD version). The other is a 2LP Box Set with a 50-page photo book in a special cover, the album on clear vinyl, a second LP containing two bonus tracks (also on clear vinyl), and a DVD featuring the music video for "Rainbow". The title track "Rainbow" on the 2LP version features an alternate mix with a different guitar solo.